Wave powered generation

ABSTRACT

Described herein are marine devices and methods that convert mechanical energy in one or more waves to mechanical energy that is better suited for conversion into electrical energy. The marine devices employ a mechanical energy conversion system that harnesses wave energy and converts it into limited motion that is suitable for input to an electrical energy generator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation and claims priority under 35 U.S.C.§120 from U.S. patent application Ser. No. 11/684,426, filed Mar. 9,2007 and entitled “Wave Powered Generation,” which claims priority under35 U.S.C. 119(e) from a) U.S. Provisional Patent Application No.60/797,974 filed May 5, 2006, and b) U.S. Provisional Patent ApplicationNo. 60/852,718 filed Oct. 18, 2006; each of these patent applications isincorporated by reference herein in its entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to devices and methods thatgenerate electrical energy. More particularly, the present inventionrelates to devices and methods that convert mechanical energy in one ormore waves to electrical energy.

BACKGROUND OF THE INVENTION

Many marine devices consume electrical power. Buoys for example includeonboard lighting and communication systems that constantly rely on anon-board power source.

Batteries are currently used to supply electrical energy to remotemarine devices such as buoys. Non-rechargeable batteries inevitably runout of energy, which necessitates inconvenient and costly batterymaintenance. Rechargeable batteries need a power source to rechargethem.

Waves offer a continuous and ample source of mechanical energy, butharnessing the wave energy for conversion into electrical energy hasbeen problematic to date. A reliable way to harness wave power andproduce electrical energy in remote marine environments would bebeneficial.

SUMMARY OF THE INVENTION

The present invention provides marine devices and methods that convertmechanical energy in one or more waves to mechanical energy that isbetter suited for conversion into electrical energy. The marine devicesemploy a mechanical energy conversion system that harnesses wave energyand converts it into constrained motion that is suitable for input to anelectrical energy generator.

In one aspect, the present invention relates to a marine device. Themarine device includes a body, a mechanical energy transmission system,and a generator. The marine device is configured such that a portion ofthe body rests above a water surface level when the marine devicefloats. The mechanical energy transmission system includes a movingportion that is configured to move relative to the portion of the bodythat rests above the water surface level in response to a water surfacelevel change. The generator is mechanically coupled to the movingportion, mechanically coupled to the portion of the body that restsabove the water surface level, and configured to produce electricalenergy using movement of the moving portion.

In another aspect, the present invention relates to a marine device. Themarine device includes a body, a mechanical energy transmission system,and a generator. The mechanical energy transmission system includes: a)an energy storage mass that is configured to move relative to the bodyin response to a water surface level change that causes movement of thebody relative to the water surface level, and b) a spring mechanicallycoupled to the energy storage mass and mechanically coupled to the body.The spring includes a stiffness that provides a resonant frequency forthe mechanical energy transmission system within about 0.2 Hertz of aresonant frequency for the marine device.

In yet another aspect, the present invention relates to a marine device.The marine device includes a body, a mechanical energy transmissionsystem, and a generator. The mechanical energy transmission systemincludes: a) a first energy storage mass that is configured to moverelative to the body in response to a water surface level change thatcauses tilting of the body relative to the water surface level, and b) asecond energy storage mass that is configured to move relative to thebody in response to the water surface level change. The generator ismechanically coupled to the first energy storage mass or the secondenergy storage mass and configured to produce electrical energy usingkinetic energy of the first energy storage mass or the second energystorage mass.

In still another aspect, the present invention relates to a buoy. Thebuoy includes a body, a mechanical energy transmission system, agenerator, and a light. The buoy is configured such that a portion ofthe body rests above a surface level of water when the buoy floats. Thelight is adapted to use electrical energy produced by the generator.

In another aspect, the present invention relates to a method ofgenerating electrical energy in a marine device. The method includesfloating the marine device on water such that a portion of the bodyrests above a water surface level when the marine device floats on thewater. The method also includes moving a portion of a mechanicaltransmission system relative to the marine device body in response to awater surface level change. The method further includes generatingelectrical energy using movement of the moving portion.

These and other features and advantages of the present invention will bedescribed in the following description of the invention and associatedfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a method overview of wave energy harvesting according tothe present invention.

FIG. 2 illustrates a simplified marine device according to oneembodiment of the present invention.

FIG. 3 shows a buoy, at two instances of wave height, in accordance withone embodiment of the present invention.

FIGS. 4A and 4B illustrates a mechanical energy conversion system thatincludes a dynamic absorber in accordance with one embodiment of thepresent invention.

FIG. 5-9 show marine devices in accordance with various embodiments ofthe present invention.

FIG. 10 shows a schematic illustration of a marine device in accordancewith another embodiment of the present invention.

FIGS. 11A and 11B illustrate a linear motion device for convertingbetween mechanical and electrical energy in accordance with a specificembodiment of the present invention.

FIGS. 12A-12C show a rolled electroactive polymer device suitable formechanical to electrical energy conversion in accordance with a specificembodiment of the present invention.

FIGS. 13A and 13B show a self-contained unit that includes a mechanicalenergy transmission system with a swinging mass designed for use with anelectroactive polymer generator in accordance with a specific embodimentof the present invention.

FIG. 14 shows marine device in front of a sea wall and configured toreceive an incoming wave normal to an axis of the marine device.

FIGS. 15A and 15B show marine device with mooring lines in tworotational positions in accordance with a specific embodiment of thepresent invention.

FIGS. 16A and 16B show a marine device in two rotational positions inaccordance with another specific embodiment of the present invention.

FIGS. 17A-17C show a breakwater generator system in accordance withanother embodiment of the present invention.

FIG. 18 shows a method of generating electrical energy in accordancewith one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described in detail with reference to a fewpreferred embodiments as illustrated in the accompanying drawings. Inthe following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art, that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process steps and/or structureshave not been described in detail in order to not unnecessarily obscurethe present invention.

Introduction

This disclosure describes marine devices that harness mechanical energyin waves for conversion to and generation of electrical energy. Thisoccurs in a two-stage process. The first stage translates mechanicalenergy in a wave, whose displacement and frequency are ofteninconsistent and unpredictable, to mechanical energy that is bettersuited for electrical/mechanical conversion. In one embodiment, thismechanical transmission translates the wave mechanical energy intomovement of an energy storage mass in one or more known directions,e.g., moving the energy storage mass along a linear slide. In anotherembodiment, a linear translation mechanism couples relative motion oftwo different parts of a marine device. For example, wave motion maycause a relative motion between a flotation element and a reaction plateor anchor; this relative displacement then serves as limited andharnessed mechanical input suitable for a generator that receives linearmotion as an input. The second stage converts the harnessed mechanicalenergy—whose direction of displacement is known and configured for inputinto a generator—into electrical energy. The electrical energy may beused and/or stored for subsequent use, as desired.

FIGS. 1-2 schematically show energy generation according to variousembodiments of the present invention. FIG. 1 shows a method overview ofwave energy harvesting and electrical energy generation according to oneembodiment of the present invention. FIG. 2 illustrates a simplifiedmarine device 10 in accordance with one embodiment of the presentinvention.

Referring initially to FIG. 1, waves 2 provide an unpredictable anduntamed supply of energy. As the term is used herein, a wave refers to achange in a water surface level. ‘Wave energy’ refers to mechanicalenergy, kinetic and/or potential, in a wave. Properties thatcharacterize mechanical energy in a wave include wave height (averagepeak to trough), wave period, wave direction, and water depth.

Marine device 10 refers to any apparatus or system that is deployed inor on water and consumes or transmits electrical energy. Many marinedevices 10 described herein float on the water such that at least aportion of the device rests above the water surface level. Twoparticular marine devices 10 will be expanded upon below: a) a marinenavigation buoy that includes a generator for powering an onboardlighting system, and b) a floating generator for general production ofelectrical energy, e.g., for supply onto a grid.

While waves offer significant amounts of energy, particularly in oceanand bay settings, their inconsistency complicates energy harvesting. Themovement 16 of a floating marine device 10 relative to the water maychange significantly between waves in terms of direction (e.g., upwardmotion for one wave, followed by angular motion of the device relativeto the water surface on the next wave, followed by angular motion in adifferent direction for the following wave, etc.), amount of motion,wave period (or frequency), etc. Wave properties will also vary withmarine environment. Waves in ocean environments are typically lowfrequency, in the 0.1 to 1.0 Hz range, and can be relatively high inamplitude (wave heights greater than 1 meter are common).

To tame and harness this input energy inconsistency, marine device 10includes a mechanical energy transmission system 15 that is configuredto convert mechanical energy in a wave (and irregular movement 16 ofdevice 10 relative to the water surface 2) to regulated mechanicalenergy 18. In one embodiment, mechanical energy transmission system 15is configured to convert a portion of the mechanical energy in a waveinto mechanical energy of an internal energy storage mass that movesrelative to the body of the marine device. For example, the mechanicalenergy transmission system 15 may transmit the wave power into movementof a mass slideably coupled to a linear slide and free to move along thesingle degree of freedom slide in response to the wave power. Energy inthe wave then goes into moving both the marine device and energy storagemass, while the latter is used as input into generator 20. In anotherembodiment, the mechanical energy transmission system 15 transmits wavepower into movement of a two portions of the marine device relative toeach other. The two portions may include a frame in the marine devicethat is fixed relative to another portion that moves in response to thewave energy. This relative motion then serves as the controlled inputinto a generator.

Mechanical energy transmission system 15 permits marine device 10 tooperate in a range of marine settings with widely varying wavecharacteristics. Suitable marine environments include open sea, bays,breakwater applications near a retaining wall, lakes, rivers and deltas,for example. Marine device 10 is well suited for use in bays where waveheights commonly vary from about 0.5 meters to about 1 meter, waveperiod varies from about 1 to about 4 seconds, and sea depth may varyfrom about 2 meters to about 40 meters. Other wave properties and marineconditions are suitable for use herein and the present invention is notlimited to any particular marine environment or wave properties.

A generator 20 converts the harnessed and regulated mechanical energyinto electrical energy 22. In one embodiment, generator 20 includes aconventional electro-mechanical generator that receives rotary orconverted linear motion from the mechanical energy transmission system15. In another embodiment, generator 20 includes one or moreelectroactive polymer generators configured to convert linear motion ofa mass in the mechanical energy transmission system 15 to electricalenergy. Other suitable conventional and non-conventional generators aresuitable for use herein and described below.

Mechanical Energy Conversion System

This section describes suitable mechanical energy transmission systemsthat translate (kinetic and/or potential) mechanical energy in a waveinto mechanical energy whose displacement and energy is limited to aknown path or range of movements, which is then available for electricalenergy generation. The mechanical energy transmission systems permit themarine device to repeatedly harvest mechanical energy in the waves,despite the inconsistency and unpredictability in wave motion and inputenergy. In one embodiment, the mechanical energy transmission systemsconvert mechanical energy outside the marine device in the environmentinto internal mechanical energy that is configured for input to agenerator.

In one embodiment, marine device 10 is a buoy. FIG. 3 shows a buoy 40 inaccordance with a specific embodiment of the present invention. Buoy 40may be remotely implemented for navigation purposes and includes one ormore lights 63 powered by a generation system.

FIG. 3 shows buoy 40 at two instances of wave height: a first waveheight 42 and a second wave height 44. First wave height 42 correspondsto a low height for water surface level 60, such as a trough of thewave, while second wave height 42 corresponds to a high wave height forwater surface level 60, such as the wave peak. Buoy 40 includes a body52, light source 63, and a self-contained generation system 46.

Body 52 includes: a tower 54 that rests above water surface 60, and abase 56 that at least partially rests below water surface 60. Lightsource 63 is attached near the top of tower 54. Buoy 40 may also includea floatation collar (or other floatation devices) to assist buoyancy andkeep light source 63 or another portion of body 52 above water surface60. Base 56 includes an internal cavity (not shown in FIG. 3) defined byouter walls.

Self-contained generation system 46 includes a mechanical energytransmission system 15 and a generator. In a specific embodiment,self-contained generation system 46 is adapted for placement on anexisting or slightly modified navigational buoy 40. In this instance,self-contained generation system 46 mechanically attaches to body 52 ofbuoy 40, such as to tower 54 or base 56, and is electrically coupled tothe electrical system on buoy 40 for supplying power to operate lightsource 63. In another embodiment, self-contained generation system 46 isdisposed in an internal cavity of base 56. As shown in FIG. 3,self-contained unit 46 is mounted on the buoy superstructure of tower54, and can be mounted on buoy 40 long after the buoy has beenmanufactured or deployed. Thus, self-contained unit 46 is a separatestructure that minimizes the changes needed to existing buoy designs.This embodiment permits adaptation of existing buoys to include localpower generation without requiring design and purchase of new buoys.Self-contained generation system 46 then allows buoy 40 operation forlong periods of time without the need for battery replacement.

FIG. 3 also shows a blow up and cross-sectional view of a particularembodiment of self-contained generation system 46, which includesmechanical energy transmission system 15 and a generator. Mechanicalenergy transmission system 15 converts mechanical energy in the water(and movement of buoy 40 on surface level 60) to kinetic energy ofenergy storage energy storage mass 64 along direction 62. In general, amechanical energy transmission system 15 of the present invention mayinclude any mechanical system that harnesses mechanical energy in a wavefor use in electrical energy harvesting. Typically this includestransmitting at least a portion of the wave motion, energy and/or powerin a wave to motion, energy and/or power of a mass along one or morepredetermined degrees of freedom (e.g., linear, rotary, combinationsthereof, etc.). This transmission reduces unpredictability of the inputwave energy and internally regulates the mechanical energy into knowndirections of displacement of the mass, which facilitates electricalenergy conversion by the generator. The present invention contemplatesnumerous designs and mechanical systems that are suitable for thispurpose. Several exemplary designs are described herein; in general,however, the present invention is not limited to these designs. In aspecific embodiment, mechanical energy transmission system 15 includes adynamic vibration absorber, which is described in more detail withrespect to FIG. 4.

For buoy 40, the mechanical energy conversion system 15 inself-contained unit 46 includes an energy storage mass 64 that isconfigured to translate linearly along a cylindrical bore or axis 66, asshown by arrow 62. Mechanical energy conversion system 15 uses movementof energy storage mass 64 along axis 66 to generate energy internal tobuoy 40 and along axis 66.

In one embodiment, energy storage mass 64 is a proof-mass, or a largeweight, configured to generate enough force for electrical energygeneration in response to waves of low frequency. The weight of mass 64,and its distance of travel along axis 66, is a matter of design choiceand may vary with the application. Factors that may affect weight ofenergy storage mass 64 and its travel distance include: the amountexpected wave energy (wave amplitude and frequency), the amount ofenergy needed by the marine device, size of buoy 40, the electricalenergy generation system used and its components and configuration, theeffective stiffness and damping characteristics of the energy transducer(electrical energy generator) that converts the linear motion of theproof-mass to electrical energy, etc. In one embodiment, energy storagemass 64 includes a mass between about 5 kg and about 300 kg. A traveldistance along axis 66 of between about 0.2 meters and about 4 meters issuitable in many applications. Other mass sizes and travel distances arealso suitable. In a specific embodiment, buoy 40 includes a mass greaterthan 100 kg or travel greater than 1 meter to produce 25 W of power attypical wave frequencies in the ocean or a bay that receives oceanwaters. Either the mass size or travel distance may be limited toimprove stability of the buoy, depending on its dimensions and size.

A generator is configured to receive motion and forces of energy storagemass 64 along axis 66, and to generate electrical energy using themotion and forces of mass 64. Electrical energy generators suitable forreceiving linear motion of mass 64 include electroactive polymers,linear induction generators and traditional electromagnetic generatorsthat first convert the linear motion of mass 64 to rotary motion inputof the electromagnetic generator, e.g., using a rack and pinion or otherlinear to rotary transmission device to convert the linear motion ofmass 64 to rotary motion.

Light sources 64 include a top light source 64 a and a central lightsource 64 b. Either light source 64 may include a halogen lamps, lightemitting diode, a prism for collecting and directing light to improve orfocus light output, or any other conventional light source and/or lightemitter.

In one embodiment, a marine device uses a dynamic vibration absorber (or‘dynamic absorber’) to improve energy harvesting. Dynamic vibrationabsorbers may be damped or undamped. First, FIG. 4A illustrates amechanical energy conversion system 15 configured to operate as anundamped dynamic vibration absorber 80 in accordance with one embodimentof the present invention.

As shown, dynamic absorber 80 includes a main mass 82, an absorber mass64, a main stiffness k1, and an absorber stiffness k2. For a marinedevice, main mass 82 represents mass of the marine device (such as thebody or hull in a buoy or breakwater generator), absorber mass 64represents the energy storage mass 64 in the mechanical energyconversion system 15, k1 represents the stiffness of the marine device(such as stiffness of the body or hull in a buoy or breakwatergenerator), and k1 represents the stiffness of the mechanical energyconversion system 15 (or stiffness along axis 66 for FIG. 3).

Looking at FIG. 4A first without the absorber mass 64 attached, aperiodic force 81, such as relative motion between the marine device andwater resultant from a wave, acts on an undamped main mass-spring system80. When the forcing frequency substantially equals the naturalfrequency of the main mass 82 and k1, the response and displacement ofmass 82 becomes theoretically infinite. This represents resonance formain mass 82.

When an absorbing mass-spring system, or ‘absorber’, that includes mass64 and k2, is attached to main mass 82 and the resonance of the absorberis tuned to substantially match that of the main mass, motion of mainmass 82 is theoretically reduced to zero at its resonance frequency.Thus, the energy of main mass 82 is apparently “absorbed” by the tuneddynamic absorber. In theory, for this undamped system, motion of theabsorber mass 64 is finite at this resonance frequency, even thoughthere is no damping in either oscillator. This is theoretically becausethe system has changed from a one degree of freedom system to a twodegree of freedom system and now has two resonance frequencies, neitherof which equals the original resonance frequency of main mass 82 (andalso absorber 64).

In one embodiment, mechanical energy conversion system 15 includes adynamic absorber (e.g., mass 64 in FIG. 3 and its associated stiffness)that is tuned to resonate at a natural frequency of a marine device (thefrequency at which the device would move with respect to the water). Ina specific embodiment, this resonance frequency matching provides aresonant frequency for mechanical energy conversion system 15 that iswithin about 0.2 hertz of a resonant frequency for the marine device 10.In a specific embodiment, this resonance frequency matching provides aresonant frequency for mechanical energy conversion system 15 that iswithin about 0.2 Hertz of a resonant frequency for the marine device 10.This resonance matching increases the motion and harvested energy forelectrical power generation provided by the mechanical energy conversionsystem 15. In addition, since the dynamic absorber also reduces motionand movement of the marine device, the mechanical energy conversionsystem also stabilizes the marine device 10. The stabilization functionis useful for a navigation buoy that requires that its light locationnot move too much.

In a specific embodiment, suitable for instances where the wave periodvaries, marine devices of the present invention actively tune theabsorber resonant frequency. This allows the mechanical energyconversion system 15 to operate at, and adapt to, multiple resonantfrequencies and conditions. In one embodiment, a component in theelectrical energy generation system contributes a stiffness thatcontrollably varies to achieve a desired resonant frequency for theabsorber. In a specific embodiment, the electrical energy generationsystem includes an electroactive polymer whose stiffness is controlledto tune the dynamic absorber. Electroactive polymers are describedbelow. In addition, further description of controlling stiffness of anelectroactive polymer is provided in commonly owned U.S. Pat. No.6,882,086, which is incorporated by reference in its entirety. Theapplied voltage and the amount of energy withdrawn at various points inthe cycle may modulate stiffness of an electroactive polymer.

Referring now to FIG. 4B, realistically, marine device 10 includes somedamping 86. Damping 86 may include interaction of the marine device 10with the surrounding water, which provides parasitic energy losses. FIG.4B shows mechanical energy conversion system 15 configured to operate asa damped dynamic absorber 85 in accordance with one embodiment of thepresent invention. In this case, the system 85 includes an effectivedamping 88 on the absorber mass 64. Damping 88 includes loses thatresult from electrical energy generation (in other words the energy thatis converted from mechanical to electrical is effectively a damping) andother mechanical energy losses in marine device 10.

Damping will create new resonance frequencies in the system. Also, afinite amount of damping for both masses 82 and 64 will reduce themotion of either mass 82 and 64 at either of the new resonancefrequencies. Often, if damping is present in either mass-spring element,the response of main mass 82 may no longer be theoretically zero at thetarget frequency.

Referring back to FIG. 3, when mechanical energy conversion system 15includes a damped dynamic vibration absorber 85 that is tuned to thenatural frequency of the marine device 10, then mechanical energyconversion system 15 decreases motion of buoy 40 and/or the anchoringstructure in two manners: a) parasitic losses via (intentional)electrical energy generation, and b) (as mentioned above) conversion ofmotion of the buoy to the absorber mass 64 via the tuned naturalfrequencies. In this manner, mechanical energy conversion system 15increases stability of buoy 40. Another way to look at buoy 40 with adynamic absorber is that some of the wave energy that normally moves thebuoy goes instead into moving mass 82 and generating electrical energy.

The previous discussion was supported by theory based on linear lumpedparameter models of the buoy and power generation devices. We do notwish to be bound by theory and further note that the system can operateeffectively even in the presence of nonlinearites due to varyingeffective masses (the effective buoy mass includes entrained water, forexample), nonlinear and time varying damping (due to the electricalpower generation or variations in the parasitic losses) and distributed(as opposed to lumped) masses of the buoy, proof mass and electricalgenerator, for example. We also note that we have so far described asystem that operates along a single axis of motion. We have designedsystems that operate with more than one direction of motion, such asmight arise from both up and down heaving and rotary rocking of a buoy.

Other mechanical energy conversion systems 15 and marine device 10designs are suitable for use herein. For example, mechanical energyconversion system 15 may be integrated into the structure of buoy 40below the waterline in base 56, structurally integrated into the bottomextending stem of base 56, or other locations on a buoy above thewaterline, below the waterline, and combinations thereof.

FIG. 5A shows a buoy 120 in accordance with another embodiment of thepresent invention. Buoy 120 includes multiple mechanical energyconversion systems located around an upper periphery of the buoy body122. Each of the mechanical energy conversion systems is included in aself-contained unit 46, situated away from the vertical center of massfor buoy 120. In FIG. 5A, buoy 120 includes four self-contained units 46aligned vertically. More or less self-contained units 46 may also beused. In addition, the self-contained units 46 and their mechanicalenergy conversion systems 15 may be disposed in other locations aboutthe buoy superstructure, which will affect the dynamic performance ofthe buoy in response to rocking and other motions.

This configuration, as opposed to a single self-contained unit 46 placedalong the vertical center of mass of a buoy as shown in FIG. 3, allowsfor the capture of not only the up and down heaving of buoy 120 in thewater, but also any angular rocking 16 of buoy 120. In pure verticalmotion, the masses 64 in each self-contained unit 46 move in phase withone another. In rocking, they move out of phase. Also, by using morethan one generator or allowing the generator to respond to rockingmotion in addition to vertical motion, marine device 120 increases theoverall power output.

FIG. 5B shows a buoy 120 that includes four self-contained units 46,each aligned at an angle relative to a vertical axis of the buoy. Thisarrangement helps each self-contained unit 46 capture and translatehorizontal motion more effectively. Cumulatively, multipleself-contained units 46, each aligned at an angle, permits buoy 120 tocapture rocking and lateral motion in any horizontal direction. Anglingthe self-contained units 46 also reduces impact on the buoy profilewhile maintaining multi-degree of freedom energy harvesting. Additionalhorizontally-aligned self-contained units 46 may also be added toharvest surge motions more effectively.

When dynamic mass absorbers are used in each self-contained unit 46,this configuration also serves to stabilize buoy 120 in both modes ofmotion. In addition, using multiple single self-contained units 46removes the reliance on a single unit and permits one to fail butmaintain electrical energy generation.

Other mechanical energy transmission systems may be used. In anotherembodiment, mechanical energy transmission system 15 includes a lineartranslation mechanism that includes a first portion such as a rod orplunger that linearly translates along or in a second portion such as acylinder. The two portions may be coupled to different parts of themarine device to harness wave energy. Typically, the different partshave relative motion caused by the wave energy and the mechanical energytransmission system 15 limits and harness that relative along the lineardegree of freedom. A linear generator then couples to the two portionsof the mechanical energy transmission system 15 and uses the relativemotion of the two portions as input for electrical energy conversion.

FIG. 6 shows a buoy 130 in accordance with another specific embodimentof the present invention.

Buoy 130 includes cables 132 that attach to the energy storage mass 64in self-contained unit 46. Cables 132 may include a suitably stiffmaterial, such as stainless steel, a chain or an abrasion resistantrope. As shown, cables 132 also extend to the mooring cables 136, whichmechanically ground the buoy 130 and prevent it from floating away.Pulleys 134 are situated on the sides of buoy 130 to localize cablemovement near the pulleys and reduce rotational forces on the buoy body.

When one or more of cables 132 is pulled taut by movement of buoy 130relative to base 138 (typically as surface level 139 rises or at thewave high points and peaks of water surface 139), at least one of thecables 132 pulls down on mass 64. Up and down heaving of buoy 120 and/orthe angular side-to-side rocking 16 of buoy 120 will then repeatedlycause one or more of cables 132 to displace mass 64 on its linear axis66. The movement of energy storage mass 64 may then be converted toelectrical energy. Since the cables now provide a propulsive force tostorage mass 64, the mass can be reduced in size. In some cases, element64 may be as simple as an attachment point that couples motion of acable 132 to motion of an electrical generator element.

FIG. 7 shows a buoy 140 in accordance with another specific embodimentof the present invention. In this case, mechanical energy transmissionsystem 15 includes cables 132 that indirectly attach the mass 64 (whichagain may be simply an attachment point) in system 15 to one or morewater brakes 142. Pulleys 144 include stiff members that keep cables 132distant from the body of buoy 140. Each water brake 142 includes a setof flat plates and a hinge that, together, act to resist upward movementbut permit downward movement of the plates (with less water resistancesince the hinge folds upwards and reduces surface area of the plateswhile moving downward). Water brakes 142 suitable for use herein arecommercially available from Magma Products of Lakewood, Calif. Otherdevices that use a deformable cup shape, or a rigid cup in place of ahinged-mechanism are also suitable for use as a water brake and arecommercially available.

Movement of buoy 140 in the water as surface level 139 changes causesrelative motion between water brakes 142 and mass 64, which attaches tothe cables, and production of electrical energy via the moving mass 64.In one embodiment, from 1 to about 6 water brakes 142 is suitable foruse with buoy 140; each water brake 142 may include from 1 to about 4cables. Another number of plates in water brakes 142 and cables 132 foreach plate are also suitable for use.

FIG. 8 shows a buoy 150 in accordance with another specific embodimentof the present invention. Buoy 150 includes a mechanical energytransmission mechanism 155 that is submerged below water line 139, andattaches directly to the bottom of buoy 150 and a water brake 152. Inthis case, water brake 152 includes a rigid plate (with no joints) thatresists both upwards and downwards motion of buoy 150. Mooring cables136 attach to the bottom of water brake 152. Mechanism 155 is configuredin this case such that movement of buoy 150 relative to base 138 isslowed by brake 152 and causes a net displacement in a component (e.g.,a plunger) in mechanical energy transmission mechanism 155 that alsocouples to the body and to an electrical generator 20.

FIG. 9 shows a buoy 160 in accordance with another specific embodimentof the present invention. Buoy 160 includes a mechanical energytransmission mechanism 165 that is also submerged below water line 139,but attaches to the mooring cable system 136. Water brake 152 includesone or more rigid plates that resist both upwards and downwards motionof buoy 150. In this instance, a mooring cable 136 a attaches to: a)buoy 160, and b) the top of mechanism 165, which attaches to water brake152, which attaches to a second mooring cable 136 b. Relative motion ofbuoy on water level 139 pulls on cable 136 a, which moves mechanicalcoupling in mechanism 165 that attaches to an inlet of an electricalgenerator.

Mechanical to Electrical Conversion

Marine device 10 includes a generator that converts mechanical toelectrical energy. The generator may include any suitable equipment tofacilitate electrical energy generation, transmission and/or storage.

FIG. 10 shows a schematic illustration of a marine device 10 inaccordance with another embodiment of the present invention. Marinedevice 10 includes generator 20, harvesting and conditioning circuitry202, battery 204, load 206 and control circuitry 208.

Generator 20 is configured to receive mechanical energy and to outputelectrical energy. As one of skill in the art will appreciate, there arenumerous technologies suitable for this task. In some instances, marinedevice 10 includes a conventional or commercially available generator 20that uses electromagnetic induction to convert mechanical energy toelectrical energy. Both AC and DC generators (or alternators) may beused. Rotary electromagnetic generators are common and often requirerotary input of the input mechanical energy. Other types of electricalgenerators exist, based on other electrical phenomena such aspiezoelectricity, and magnetohydrodynamics, and are suitable for usewith marine device 10. Electroactive polymers are also well suited foruse and described in further detail below.

In one embodiment, generator 20 is selected and configured to generatebetween about 5 joules and about 60 joules per stroke of a mass inmechanical energy transmission system 15. In a specific embodiment,generator 20 is selected and configured to generate between about 20joules and about 30 joules per stroke of the mass. 20 joules per stroketranslates to about 5 to about 10 watts of power at typical bay wavefrequencies. Of course, the size of generator 20 will vary with thenumber of mechanical energy transmission systems 15 used, the size ofthe mass(es) in each system 15, amount of energy in the waves, waveperiod, desired electrical energy performance of marine device 10, etc.

Harvesting and conditioning circuitry 202 includes any circuitryconfigured to perform one or more of the following tasks: energyharvesting, voltage step-up or step-down, conversion between AC and DCpower, smoothing voltage, priming the system with a voltage for startup,conditioning power output for an electrical load or the power grid,emergency shut-down, storing energy from the generator to provide outputpower during periods of low wave activity, communicating faultconditions (e.g. if the generator is not working properly), and adaptingthe system to compensate for unexpected or expected generator failuremodes (e.g. loss of one of several electroactive polymer devices eitherunexpectedly or expected as a result of graceful lifetime decay. In somecases, harvesting and conditioning circuitry 202 includes circuits andsoftware that allows components on marine device 10 to adapt to varyingwave conditions, such as tuning stiffness in a mechanical energytransmission system 15 to obtain a dynamic absorber. Circuitry 202 mayalso be configured to efficiently harvest the energy from generator 20despite unknown input frequencies and amplitudes, and that depend on themechanical transmission system 15 and generator 20 selected. Forexample, an electroactive polymer may introduce nonlinear varyingelectrical properties that are managed by conditioning circuitry 202.Harvesting and conditioning circuitry 202 may also provide a smallvoltage for initial startup, if needed.

For electroactive polymers used in generator 20, harvesting andconditioning circuitry 202 may include circuitry designed to manage:high voltages, fast response times, polymer current loading andunloading, or other performance characteristics associated withelectroactive polymers.

Battery 204 stores electrical energy for later use. Rechargeablebatteries are thus well suited for use, such as any conventional andcommercially available battery.

Load 206 generally includes any device or system that consumeselectrical energy. Load 206 will vary with the marine device. For anavigation buoy, load 206 typically includes one or more lights. Othertypes of buoys may require energy to power sensors, computers and radiotransmissions, for example. Marine generators deployed for electricalenergy harvesting and provision onto a grid may include energymonitoring, device health monitoring, and/or communication resources.

Marine device 10 may also include control circuitry 208, which includesany combination of hardware and/or software for one or more controllingcomponents on marine device 10. For example, control circuitry 208 maymanage the power output between flashing lights 206 and rechargingbatteries 204.

Control circuitry 208 regulates switches 210, which control the movementof electrical energy in marine device 200. In one embodiment, controlcircuitry 208 includes a processor and memory, where the memory includessoftware with instructions that enable processor to execute methods ofelectrical energy generation described herein.

In one embodiment, the generator is partially or fully included in aself-contained unit 46. For example, one or more electroactive polymertransducer rolls may be attached to mass 64 in FIG. 3 and wrapped aroundaxis 66; the electroactive polymer transducer rolls then get longer andshorter as the mass 64 moves. In another embodiment, a push rod or othermechanical coupling attaches to the mass 64, for example.

Electroactive Polymers

In one embodiment, the marine device employs an electroactive polymertransducer, with compliant electrodes coupled thereto, as a generator.The electroactive polymer transducer offers various design advantagescompared with generators based on conventional technologies such asrotary electromagnetic generators operated through mechanicaltransmissions.

Dielectric elastomer transducers are one suitable type of electroactivepolymer and include a relatively soft rubbery polymer disposed betweentwo compliant electrodes. Dielectric elastomer transducers may operatein actuator mode, generator mode, and/or sensor mode, depending onconfiguration and their driving circuitry. The stiffness for andielectric elastomer transducer may also be controlled.

Other types of electroactive polymers suitable for use herein includeelectostrictive polymers such as co-polymers of PVDF or semi-crystallinepolyurethanes, piezoelectric polymers such as PVDF, ionically-conductivepolymers, and liquid crystal elastomers.

Dielectric elastomers in the actuator mode convert electrical tomechanical energy because an electric field pressure (applied using theelectrodes) acts to exert work on the material and load. Electrically,the actuator mode brings opposite charges closer together and likecharges farther apart as the polymer film contracts in thickness andexpands in area. These changes reduce the stored electrical energy, andthe difference is converted to mechanical work. Further description ofelectroactive polymer actuation is provided in commonly owned U.S. Pat.No. 6,781,284, which is incorporated by reference herein in itsentirety.

In the generator mode, electrical charge is placed on the electroactivepolymer transducer in a stretched state. When the polymer contracts,elastic stresses in the film (which may be assisted by external loads)work against the electric field pressure of any charge on theelectrodes, thus increasing electrical energy of the charge. On amicroscopic level, charges on opposite electrodes separate as the filmthickness increases, while like charges on the same electrode compresstogether as the polymer area contracts. Electrically, these changesraise the voltage of the charge, which increases (and generates)electrical energy. Further description of electroactive polymergeneration is provided in commonly owned U.S. Pat. No. 6,768,246, whichis incorporated by reference herein in its entirety.

Portions of an electroactive polymer device may also be configured toprovide variable stiffness. As mentioned above, this may be used to tunea dynamic absorber to increase mechanical energy harvesting, reducemarine device 10 motion, and increase marine device 10 stability.Systems employing an electroactive polymer transducer offer severaltechniques for providing stiffness control. In one embodiment, open looptechniques are used to control stiffness of a device employing anelectroactive polymer transducer, thereby providing simple designs thatdeliver a desired stiffness performance without sensor feedback. Forexample, control electronics in electrical communication with electrodesof the transducer may supply a substantially constant charge to theelectrodes. Alternately, the control electronics may supply asubstantially constant voltage to the electrodes. Closed-loop stiffnesscontrol may be used to adaptively tune a dynamic absorber—reactively andin real time—to the natural frequency in a marine device. Exemplarycircuits for providing stiffness/damping control are provided incommonly owned U.S. Pat. No. 6,882,086.

Some electroactive polymer transducers include large strain capabilitiesthat can be well matched to ocean wave motion allowing a robustmechanical conversion mechanism with few moving parts. Electroactivepolymer transducers are well suited for low frequency or variable speedmechanical input. For these scenarios, conventional generators rely ontransmissions with their added cost, complexity, and size, which may notbe necessary for electroactive polymer transducers. Linear, as opposedto rotary motion, also favors electroactive polymer transducers.Electroactive polymer transducers are thus very useful when themechanical input is intrinsically low frequency and/or variable speed,as in many marine environments.

For many electroactive polymer transducers, higher operating voltagesincrease the amount of energy that can be generated for a given amountof material. Voltages of 100 V to 5 kV, corresponding to electricalfields within the polymer of up to 100 MV/m or more, are typical.Electronic circuit designs have been developed for both stepping up lowvoltages to high voltages, and for stepping down high voltages to lowvoltages. Many basic circuit designs have been adapted from otherapplications, such as voltage conversion circuits for fluorescentlights, and are low cost and reliable.

Electroactive polymers can be implemented into a wide variety oftransducers and devices. Exemplary devices include rolls, linear motiondevices, and diaphragm devices. Many of these transducers, such as aroll, can package a large amount of material into a compact shape. U.S.Pat. No. 6,781,284 describes several transducers and devices suitablefor use herein.

FIGS. 11A and 11B illustrate a linear motion device 230 for convertingbetween mechanical and electrical energy in accordance with a specificembodiment of the present invention. Linear motion device 230 is aplanar mechanism having mechanical translation in one direction, 235.The linear motion device 230 comprises an electroactive polymer 231having a length 233 greater than its width 234. In a specificembodiment, polymer 231 includes a 2:1 length to width ratio.

Polymer 231 is attached on opposite sides to stiff members 232 of aframe along its length 233. Stiff members 232 have a greater stiffnessthan the polymer 231. The geometric edge constraint provided by stiffmembers 232 prevents displacement in a direction 236 along polymerlength 233 and facilitates deflection in direction 235. In somedielectric elastomers, such as acrylics, it is desirable to prestrainthe polymer material in order to get it to the desired thickness andstiffness. When linear motion device 230 is implemented with a polymer231 having anisotropic pre-strain, such as a higher pre-strain in thedirection 236 than in the direction 235, then polymer 231 is stiffer inthe direction 236 than in direction 235 and large deflections indirection 235 are permissible. By way of example, such an arrangementmay produce linear strains of at least about 200 percent for acrylicshaving an anisotropic pre-strain.

Linear motion device 230 is well suited to receive motion of energystorage mass 64 along a linear slide 66 in self-contained unit 46 ofFIG. 3, for example. Charge is then added to and removed by controlcircuitry according to the position of mass 64 as it stretches andcontracts polymer 231.

Electroactive polymers may also be rolled to increase the amount ofpolymer in a confined space. FIGS. 12A-12C show a rolled electroactivepolymer device 320 suitable for mechanical to electrical energyconversion in accordance with a specific embodiment of the presentinvention. FIG. 12A illustrates a side view of device 320; FIG. 12Billustrates an axial view of device 320 from its top end; FIG. 12Cillustrates an axial view of device 320 taken through cross section A-A.Device 320 comprises a rolled electroactive polymer 322, end pieces 327and 328, and spring 324.

FIG. 12C shows the rolled layering of electroactive polymer 322. Arolled electroactive polymer may include an electroactive polymer with,or without electrodes, wrapped round and round onto itself (e.g., like ascrolled poster) or wrapped around another object (e.g., spring 324).For single electroactive polymer layer construction, a rolledelectroactive polymer of the present invention may comprise betweenabout 2 and about 200 layers. Polymer 322 and spring 324 are capable ofaxial deflection between their respective bottom top portions.

End pieces 327 and 328 are attached to opposite ends of rolledelectroactive polymer 322 and spring 324. Endpiece 327 has an inner hole327 c that includes an internal thread capable of threaded interface anddetachable mechanical attachment with a threaded member, such as a screwor threaded bolt.

Many electroactive polymers perform better when prestrained. Forexample, some polymers exhibit a higher breakdown electric fieldstrength, electrically actuated strain, and energy density whenprestrained. Spring 324 of device 320 provides forces that result inboth circumferential and axial prestrain for polymer 322. Spring 324 isa compression spring that provides an outward force in opposing axialdirections (FIG. 12A) that axially stretches polymer 322 and strainspolymer 322 in an axial direction. Thus, spring 324 holds polymer 322 intension in axial direction 335.

Rolled electroactive polymer devices allow for compact electroactivepolymer device designs. The rolled devices provide a potentially highelectroactive polymer-to-structure weight ratio, and can be configuredto actuate in many ways including linear axial extension/contraction,bending, and multi-degree of freedom actuators that combine bothextension and bending. A rolled electroactive polymer is well suited foruse in self-contained unit 46 of FIG. 3. The polymer may be wrappedaround the energy storage mass 64 and linear slide 66, which provides acompact form factor for self-contained unit 46 with numerous layers ofelectroactive polymer.

Other electroactive polymer devices are also suitable for use herein. Ingeneral, electroactive polymer transducers are not limited to anyparticular geometry or linear deflection. For example, a polymer andelectrodes may be formed into any geometry or shape including tubes androlls, stretched polymers attached between multiple rigid structures,stretched polymers attached across a frame of any geometry—includingcurved or complex geometries, across a frame having one or more joints,etc. Deflection of a transducer according to the present inventionincludes linear expansion and compression in one or more directions,bending, axial deflection when the polymer is rolled, deflection out ofa hole provided in a substrate, etc. Deflection of a transducer may beaffected by how the polymer is constrained by a frame or rigidstructures attached to the polymer.

In one embodiment, marine device 10 uses one or more commerciallyavailable electroactive polymer devices, such as those available fromArtificial Muscle (AMI) of Menlo Park, Calif. In particular, AMIprovides a universal muscle actuator, which is suitable for use herein.The universal muscle actuator includes two opposing diaphragm actuatorsattached to a common central platform. The narrow annular area of eachdiaphragm effectively couples much of the actuation stress to thecentral platform. Universal muscle actuators have been made in a rangeof sizes. The number of layers of the diaphragms may vary as well. Whiledeveloped as an actuator, the universal muscle actuator may also operateas a generator. A universal muscle actuator employed as a generator mayinclude a larger diameter to allow for the needed energy output.

A collection of electroactive polymer devices may be mechanically linkedto form a larger generator with a common output, e.g. force and/ordisplacement. By using a small electroactive polymer as a base unit in acollection, conversion between electric energy and mechanical energy maybe scaled according to an application by connecting many individualelements in parallel or series.

The buoy-mounted generator design of FIG. 5 may employ a long and narrowform factor for the electroactive polymer device(s). Vertically stackedelectroactive polymer devices, such as rolled devices or universalmuscle actuators, are two suitable electroactive polymer approaches withsuch a long and narrow form factor. This approach is also suitable foruse in mooring cables where the electroactive polymer device is disposedalong the mooring cable and protected by a sheath.

The amount of electroactive polymer included in a marine device willdepend on the amount of desired power for the marine device. In oneembodiment, about 1 meter square of electroactive polymer film is usedfor each watt of power output desired. Thus, for typical wavefrequencies, a 25-watt generator would employ about 25 m² ofelectroactive polymer. If, for example, the marine device 40 of FIG. 3uses universal muscle actuators with an outer diameter of 30 centimetersand an inner diameter of 10 centimeters, each single-layer universalmuscle actuator is about 0.063 m². This amounts to about 400 of thesedevices for 25 watts. Alternatively, if each universal muscle actuatorincludes ten layers of electroactive polymer, then the marine device 40of FIG. 3 may only use 40 UMA devices. For the four self-contained unit46 design of marine device 120 of FIG. 5, then each unit 46 only contain10 universal muscle actuator devices.

In order to increase energy density with dielectric elastomers, energygeneration may be typically done at high voltage (1 kV or more). In oneembodiment, an electroactive polymer generator system that is used torecharge a battery, for example, includes both step-up and step-downvoltage conversion. Suitable description of step-up and step-downvoltage conversion suitable for use with electroactive polymergeneration is provided in commonly owned U.S. Pat. No. 6,768,246. Thiscircuitry may be added to harvesting and conditioning circuitry 202 ofFIG. 10.

Electroactive polymer generators may employ harvesting and conditioningcircuitry 202 configured for their electrical performance. Two suitablecircuit designs include inductive circuits and capacitive circuits. Inthis case, circuitry 202 harvests and conditions the energy provided byAC swings in electroactive polymer voltage and energy using inductiveand/or capacitive elements. In general, electroactive polymer generatorcircuits are designed so that, at least on average and ideallythroughout the cycle, the electroactive polymer voltage at a givenelectroactive polymer strain is lower when it is expanding than when itis contracting.

Inductive circuits switch stored electrical energy in an electroactivepolymer back and forth between a buffer capacitor and through aninductor at the appropriate time in the generator's cycle. Theelectroactive polymer acts as a capacitor in this case. As one of skillin the art will appreciate, directly switching the energy from onecapacitor at higher voltage to another capacitor at lower voltage isinefficient unless the two capacitors happen to be close in voltage. Byusing an inductor in the circuit, transfer of energy between capacitorsat different voltages may be accomplished efficiently, even when theyare at greatly different voltages. The inductor circuit works byinitially charging the buffer capacitor and electroactive polymer to anominal, low level. The buffer capacitor is typically much larger incapacitance than the expected peak electroactive polymer capacitance.When the electroactive polymer is stretched, its voltage drops and oneswitch is closed to allow charge and energy from the buffer capacitor toflow into the electroactive polymer through the inductor. A diode may beused to prevent back flow of energy. The electroactive polymer is thencontracted by the external mechanical wave energy and mechanical energytransmission system, thereby reducing its capacitance and increasingboth the voltage and energy on the electroactive polymer. A secondswitch (on a second conduction path) is then closed to allow energy andcharge to flow from the electroactive polymer (which now has a highervoltage than the buffer capacitor), through the inductor, and into thebuffer capacitor. A second diode may be used to prevent back-flowthrough the second conduction path. The inductor efficiently transfersthe energy, including the increase in electrical electroactive polymerenergy from contraction, to the buffer capacitor. To do this, a thirddiode is provided to allow the inductor to pull additional charge upfrom ground (or the low or negative side of the circuit) to the highside of the buffer capacitor in a manner analogous to a buck circuitknown to one of skill in the art. If the energy gain of theelectroactive polymer from contraction was sufficient to overcomeparasitic losses in the circuit, the buffer capacitor gains an increasein stored electrical energy. This additional electrical energy can beused to power a load, or used to further raise the voltage of both thebuffer capacitor and electroactive polymer to reach a more optimaloperating point. The switches in this circuit can be transistorswitches, mechanical switches, or other efficient switches known to oneof skill in the art.

Capacitive circuits may be designed and implemented in various ways. Onesimple version uses a coupling capacitor in electrical communicationwith the high side of an electroactive polymer on one terminal, and thehigh side of a buffer capacitor on the other side of the terminal. Afirst diode prevents backflow of energy from the coupling capacitor tothe buffer capacitor. A second diode connects from ground directly tothe coupling capacitor's terminal opposite the electroactive polymer(i.e., to the same terminal that connects to the first diode but betweenthe first diode and the coupling capacitor). With this arrangement, whenthe electroactive polymer side of the coupling capacitor is exposed toAC voltage (provided by the stretching and contracting of the chargedelectroactive polymer), the opposite side of the coupling capacitorpulls charge up from ground when the electroactive polymer side goes lowin voltage (electroactive polymer stretched), and pushes charge onto thebuffer capacitor when the electroactive polymer side goes high involtage (electroactive polymer contracted). The circuit acts like acharge pump. To maintain electroactive polymer charge in the presence ofparasitic losses (such as leakage through the electroactive polymer), athird diode can be connected to the high side of the electroactivepolymer from the buffer capacitor to allow charge to flow onto theelectroactive polymer whenever its voltage drops below the buffercapacitor voltage. With this arrangement, if no charge is taken off thebuffer capacitor and the electroactive polymer energy gain issufficient, the buffer capacitor will increase in voltage as theelectroactive polymer is cycled, and the third diode allows theelectroactive polymer to increase overall voltage correspondingly. Thesystem becomes self-pumping, and only requires a small amount ofinitially input energy and voltage to reach a high voltage and storedenergy. This can be provided, for example, by a battery, and a fourthdiode can be used to prevent backflow to the battery. Once the buffercapacitor and a fourth diode reach a desired operating voltage, variousadditional circuits may withdraw energy from the buffer capacitor tomaintain a desired power output without an additional increase inoverall system voltage. Many modifications are possible with thiscircuit, such as additional stages of charge pumping to allowself-pumping even when the various additional circuits voltage gain orAC amplitude is small. Another useful embodiment is to include seriescapacitors in place of the buffer capacitor with appropriate switchingand diodes to provide lower voltage output, or to connect the buffercapacitor to an inductive step-down buck circuit for the same function.

Harvesting and conditioning circuitry 202 for an inductive circuitswitches the electroactive polymer voltage on/off. This switching may bedone with mechanical contacts or electrically with a control signal, forexample. The mechanical contacts may be arranged at maximum and minimumstroke positions to automatically inform the system of stroke status atthese points. Switching with high-voltage transistors is also suitable.Sensors that indicate when the electroactive polymer is at its extremepositions may also be used.

The inductive circuit works more efficiently when the electroactivepolymer stretches and contracts a large amount. Various mechanicaltransmission schemes and/or electrical tuning can be configured to helpone or more electroactive polymers operate at large strain conditions.For example, a mechanical energy transmission system 15 may beconfigured to allow for lower stiffness and fast electroactive polymerresponse.

FIGS. 13A and 13B show a self-contained unit 340 that includes amechanical energy transmission system with a swinging mass 352 designedfor use with an electroactive polymer generator 350 in accordance with aspecific embodiment of the present invention.

In this case, movement of the marine device results in back and forthswinging of mass 352 about a pivot 356. Self-contained unit 340 providesa negative spring constant using an inverted pendulum or over-centermechanism when a spring is added. Electroactive polymer 350 couples to apendulum arm 354, attached to mass 352, such that electroactive polymer350 deflects as mass 352 swings. Deflection of electroactive polymer 350is used to generate electrical energy. Also, electroactive polymer 350provides stiffness to the system, including a controllable stiffness insome embodiments, as described above.

This self-contained unit 340 converts both up and down and tilting (orrocking) motion of a marine device 10 in the water into motion of mass352. In other words, self-contained unit 340 provides a means ofcoupling angular and lateral motion (in addition to vertical motion) ina single device. Self-contained unit 340 also provides frequencydoubling (the electroactive polymer 350 stretches and relaxes twice whenthe pendulum goes through top point), which is of use in low frequencywave environments. A slack cable 358, attached to inverted pendulum,adds a non-linear spring that allows for fast expansion and contractionof electroactive polymer 350, thereby reducing leakage losses in theelectroactive polymer. Frequency doubling allows a single wave cycle toproduce two cycles of expansion and contraction of the electroactivepolymer 350. Thus, only half the amount of electroactive polymermaterial would be needed to produce the same power output (alternativelythe same amount of material could be operated at a lower voltage orstrain).

The electrical power generated by an electroactive polymer generator istypically at high voltage. The high voltage electrical energy can be:used directly (such as for flashing lights), stored at a high voltage ona capacitor, and/or to recharge batteries. The electronic generationcircuit may also include the ability to step-down the high voltage. Asimple inductive step-down circuit known as a “buck” circuit is suitablefor step-down in many instances.

Other Marine Devices

This section describes other marine devices and applications that maybenefit from a mechanical energy transmission system 15 and generator20.

One such marine device is a marine generator deployed specifically forelectrical energy production. For generators located near a shore, wavepower can be used to supply energy to installations located near theshore. These installations might include navigational lighting locatedon seawalls or breakwaters. The electricity could also be used to supplyindustries that are located near the shore or on islands and thusrelieve the need to transmit electricity long distances or over water.Wave power, since it does not require any fuel source or produce anyeffluents, can also be used to supply clean energy for general needs.

The location of the wave power electrical generation device near anexisting or planned breakwater or seawall is attractive because thefunctions are complementary. The wave power device will tend to calm thewaves hitting the seawall or breakwater. The breakwater or seawall canhelp amplify the waves of the device since some waves are reflected. Theseawall or breakwater also can serve as a desirable anchor point for thegenerator device.

In one specific application, the marine device is a floating breakwatergeneration device that harvests power in large waves found in deep-waterareas of a coastline or near an existing breakwater or similar seawallstructure in shallower waters. For the Japanese coastline for example,these waves frequently include a 2-meter peak-to-trough average waveheight with a 7 to 8 second period. A marine generator as describedherein may also be located adjacent to existing or specially madeseawalls and breakwaters in other locations. Because of its location,the marine generator may also help protect the seawall or breakwaterfrom erosion.

Electrical power from the generator may be used to power navigationallighting on the nearby seawall or breakwater—or used for a variety ofgeneral needs, such as supply onto an electrical grid. For supply onto agrid, the marine device also includes a tether or other form ofelectrical communication that transports the generated electrical energyfrom the floating marine device to a gird connection. The power may alsobe used to power other marine or aviation navigational aids, generatepower for nearby buildings, or for transmission to more remotelocations.

FIGS. 14-15 show a marine device 400 in accordance with a specificembodiment of the present invention. FIG. 14 shows marine device 400 infront of a sea wall 404 and configured to receive an incoming wave 405 anormal to a long axis of the marine device 400. FIGS. 15A and 15B showmarine device 400 with mooring lines 420 for two rotational positions ofmarine device 400 in accordance with a specific embodiment of thepresent invention.

As mentioned above, many marine devices described herein may include amechanical transmission system that does not include an energy storagemass that moves relative to the body for electrical energy harvesting.In this case, the breakwater generator device 400 generates electricalenergy using wave power, and includes a mechanical energy conversionsystem that includes a floatation chamber 402 coupled to mooring lines420.

Flotation chamber 402 is configured such that device 400 at leastpartially floats on water. Flotation chamber 402 converts the waveenergy into mechanical energy along one or more known directions,namely, the rotation of flotation chamber 402 about its long axis(normal to the page in FIG. 15A). Flotation chamber 402 may include aninflatable plastic or foam coated with concrete or plastic, for example.The outer shape of flotation chamber 402 reacts to wave motion andchanges in the surface level of water on which the generator device 400floats. In this case, flotation chamber 402 includes an axial profileshown in FIG. 15 a that reacts to water surface level changes movingnormal to the axis (see FIG. 14). An incoming wave thus causes flotationchamber 402 to rotate about its long axis and tilt back and forth, asshown in FIGS. 15A and 15B.

Mooring lines 420 attach to front and back portions of flotation chamber402 on opposite sides of the center of mass of flotation chamber 402.Rotation of flotation chamber 402 about its axis causes mooring lines420 to stretch and contract (see FIGS. 15A and 15B). In a specificembodiment, mooring lines 420 couple to an electromagnetic electricalenergy generation system. For example, mooring lines 420 may couple toelectromagnetic generators at the sea floor where they are anchored. Inanother specific embodiment, mooring lines 420 each include one or moreelectroactive polymer generators that convert linear deflection ofmooring lines 420 into electrical energy. In this case, and as shown inFIG. 15A, mooring lines 420 include a rigid cable that couples to thebottom of an electroactive polymer device that couples at it top end toanother rigid cable and flotation chamber 402. Rolled electroactivepolymers are suitable for use in mooring lines 420. Concatenatedelectroactive polymers may also be stacked in series to provideelectroactive polymer devices with lesser length. In this case, a rubberor metal sealed bellows may be added to mooring lines 420 to cover, sealand protect the electroactive polymer devices.

By using mooring lines 420 a and 420 b on opposing sides of eachflotation chamber 402 (see FIG. 15A), and on opposing ends (see FIG.14), the electroactive polymer devices can stretch and contract withseveral different motions of chamber 402 (height increase, rolling andtilting, for both incoming waves 405 a and transverse waves 405 b,etc.), allowing device 400 to generate power with almost any wavedirection and water surface level change.

FIGS. 16A and 16B show a marine device 400 b in two rotational positionsin accordance with another specific embodiment of the present invention.Marine generator 400 b includes an internal electroactive polymer 430that separates two internal cavities 432 and 434. Internal cavity 432includes a liquid 436, such as water. Rotation of marine device 400 b—inresponse to changing surface levels of the water or a passing wave asshown—causes the marine device 400 b to rotate and liquid 436 to move inchamber 432 so as to intermittently push on electroactive polymer 430(FIG. 16A), which causes polymer 430 to expand.

Electrical control circuitry then monitors the state of deflection ofpolymer 430, and adds and removes current to and from polymer 430according to the deflection state of polymer 430. In a specificembodiment, the electroactive polymer 430 communicates with circuitrythat senses the deflection state of polymer 430. Sensing using anelectroactive polymer is described in commonly owned U.S. Pat. No.6,809,462, which is also incorporated by reference in its entiretyherein for all purposes.

Another embodiment of marine device 400 b includes liquid 436 in thesecond cavity 434. This allows the liquid 436 to push on polymer 430when in the position shown in FIG. 16B, which powers polymer 430 forrotational movement of marine device 400 in both clockwise andcounterclockwise directions.

In another embodiment of marine device 400 b, internal cavities 432 and434 form outer cavities about an inner cavity in marine device 400 bthat internally includes liquid 436. In some cases, this may doublemechanical energy transmitted to the polymer (and potentially double theelectrical energy harvested).

A marine generator 400 may include both electroactive polymer 430 andmooring lines 420. This allows the device 400 to generate electricalenergy for almost any chamber 402 motion including any translation orrotation of the device. This includes waves that move normal 405 a tothe wall 404 from the front or reflect from behind, as well astransverse waves 405 b (FIG. 14).

In another embodiment using a movable liquid, the rotation of the device400 b causes the liquid 436 to flow through a turbine attached to aconventional rotary electromagnetic generator.

FIGS. 17A-17C show a breakwater generator system 450 in accordance withanother embodiment of the present invention. FIG. 17A shows aperspective view of system 450; FIG. 17B shows a side view of twoadjacent generators 452 used in system 450; and FIG. 17C shows a topview of interconnection between generators 452 in system 450.

Referring first to FIG. 17B, each generator 452 includes a frame 454,water brake 456, float 457, and at least one mechanical energytransmission system 455.

Water brake 456 attaches to a bottom portion of frame 454, rests underwater surface level 458 when the generator is deployed, and resistsvertical motion of each generator 452.

Mechanical energy transmission system 455 a is vertically aligned withrespect to frame 454 and includes a portion that mechanically couples towater brake 456 and a second portion that mechanically couples to aportion of frame 454 that rests above the water surface level 458. Achanging water surface level 458 creates differential vertical motion inmechanical energy transmission system 455 a, and a generator attachedthereto. In one embodiment, mechanical energy transmission system 455 aincludes a rod that mechanically couples to water brake 456 andvertically translates relative to frame 454. This relative motion isused to generate electrical energy with a generator coupled to a portionof mechanical energy transmission system 455. For example, one portionof an electroactive polymer may be coupled to the rod in mechanicalenergy transmission system 455 while another portion of theelectroactive polymer couples a stationary portion of mechanical energytransmission system 455 (stationary relative to frame 454) or to frame454. In a specific embodiment, frame 454 includes a metal or stiffplastic, while water brake 456 may include coated styrofoam, a metal,stiff polymer, fiberglass or cement for example.

Generator system 450 also harvests relative motion between generators452. A lattice structure mechanically couples generators 452 in system450, and is shown from the top in FIG. 17C. The lattice structureincludes an array of connectors 460. In this case, the connectors 460are linear and couple two adjacent generators 452; other connectiondesigns are also suitable for use. One or more linear connector 460 inthe lattice structure includes a mechanical energy transmission system455 that couples to two adjacent generators 452 such that relativemotion between the adjacent two generators 452 deflects two portions ofthe mechanical energy transmission system 455 with relative motion. Forexample, a rod or one end of transmission system 455 may mechanicallycouple to the frame 454 of a first generator 452 while a plunger or theother end of transmission system 455 mechanically couples to the frame454 of a second adjacent generator 452. Relative lateral motion betweenthe adjacent generators 452 then causes deflection in mechanical energytransmission system 455, which may then be harvested along its knowndeflection for electrical energy production.

The lattice in system 450 is suitable to capture motion via: a) relativelateral motion between generators 452 (e.g., in a plane horizontal tothe water), b) relative rocking motion between generators 452, c)relative vertical motion between generators 452, and d) combinationsthereof. Since wave motion is generally unpredictable, an advantage ofsystem 450 is that it harvest three dimensional motion in the wavesregardless of the direction of motion, which allows the system toharvest wave energy despite the unpredictability of the wave motion andits affect on the individual generators 452.

System 450 is modular. This allows system 450 to be easily scaled in thenumber of generators 452—and aggregate electrical output—to a particularapplication. FIG. 17A shows a continuum of generators 452, which mayextended in length to form long chains, as desired. Generators 452 mayalso be replicated to form large area “patches” that are severalgenerators 452 wide, as well as several generators long. The size andshape of system 450 may also be adapted to local topography and waveconditions. For example, adding generators 452 increases reaction forceson mechanical energy transmission system 455 due to inertial effects ofthe entire system, which permits greater electrical energy production inrough marine environments.

In one embodiment, system 450 includes a redundant number of generators452. This redundant design permits system 450 to: a) harvest more energyfrom a given area of the sea, and/or b) harvest less energy but includefault tolerance in system 450 to accommodate one (or more) generator 452malfunctions.

System 450 may also be expanded upon or repaired after initialdeployment. Self-contained units 46 and many other moving parts in eachgenerator 452 are located above the water line 458, where they can beeasily built or serviced (including replacement).

The breakwater generators 400 and 450 may be flexibly located. Placementin front of an existing breakwater or seawall 404 allows the generator400 to make use of reflected waves for added response. Breakwatergenerator 400 is also modular and thus able to operate one small unit ormany units depending on power needs; flotation chambers 402 and mooringcables 420 can be added in series along the wall 404 to allow fordifferent amounts of power generation. Additional lines may also bedisposed in parallel lines in a direction normal to wall 404. System 450has a similar number of mooring options. Each water brake 456 can bemoored to the seafloor or breakwater or only a few of the water breakscould be moored to the sea floor.

Other marine devices that may benefit from a mechanical energytransmission system and generator described herein include guides for ashipping lane, wave attenuators that are configured to diminishing waveenergy, floating barriers, or any floating marine device.

Methods

The present invention also relates to methods of generating electricalenergy in a marine device. FIG. 18 shows a method 500 of generatingelectrical energy in accordance with one embodiment of the presentinvention.

Method 500 begins with floating the marine device such that a portion ofthe body rests above a water surface level when the marine device floatson the water (502). The marine device includes a mechanical energytransmission system and a generator. In one embodiment, the mechanicalenergy transmission system and generator are included in aself-contained unit that is added to the marine device long after itsinitial deployment. In a embodiment, the marine device is custom madewith the mechanical energy transmission system and generator addedduring manufacture. The marine device is configured such that a portionof its body rests above a surface level of water when the marine devicefloats in the water.

Electrical energy generation method 500 then occurs when the watersurface level changes and a portion of a mechanical transmission systemmoves relative to the marine device body in response to the watersurface level change (504). As described above, the moving portion mayinclude a proof mass or a rod (e.g., attached to a water brake in thewater) that moves relative to the marine device body when the watersurface level changes. For example, the marine device may rise when thewater surface level rises, albeit at different rate or to differentlevel than the moving portion. Alternatively, the marine device may tiltwhen the water surface level changes, which causes differential motionin the proof mass or rod relative to the body. Tilting in this senserefers to any rotation or rocking of the device from its position beforethe wave disturbance.

An energy storage mass or rod moves relative to the body typicallybecause there is a degree of freedom between the energy storage mass orrod and the marine device body. In one embodiment, the energy storagemass moves along a single degree of freedom, such as a linear slide orvia a rotational joint. In another embodiment, a stiffness associatedwith the energy storage mass is designed and configured such thatresonant frequency of the mechanical energy transmission system is aboutequal to the marine device. This dynamic vibration absorption increasesmotion of the energy storage mass—which increases the amount ofharnessed mechanical energy available for conversion to electricalenergy. In another specific embodiment, the stiffness is tunable andmatched reactively in real time by a control circuit to provide aresonant frequency for the mechanical energy transmission system that isabout equal to the marine device.

Many of the mechanical energy transmission systems and generatorsdescribed above are suitable to capture and convert wave energy despitethe variance and inconsistency in water surface level changes betweenwaves. The present invention is thus well suited to handle varying andinconsistent water surface level movements and waves with varyingproperties, such as those found in choppy water conditions.

Electrical energy is then generated using relative motion between themoving portion and the marine device body (506). Various generatorssuitable for use herein were described above. The electrical energy maybe used immediately, converted in voltage, and/or stored for subsequentuse.

In other embodiments an energy storage mass 506 is not used. Instead,the waves produce a displacement between two components of a lineartransmission mechanism. This linear displacement is used to generateelectricity with a generator coupled to accept the linear motion asmechanical input.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents thatfall within the scope of this invention which have been omitted forbrevity's sake. By way of example, although the present invention hasbeen described in terms of several polymer materials and geometries, thepresent invention is not limited to these materials and geometries. Itis therefore intended that the scope of the invention should bedetermined with reference to the appended claims.

1. A marine device comprising: a body, wherein the marine device isconfigured such that a portion of the body rests above a water surfacelevel when the marine device floats and configured such that the watersurface level change causes movement of the body relative to the watersurface level; a mechanical energy transmission system including anenergy storage mass, slideably coupled to a linear axis, and configuredto linearly translate relative to the portion of the body that restsabove the surface level of water and at an angle relative to the watersurface level in response to a water surface level change; and agenerator mechanically coupled to the moving portion and to the portionof the body that rests above the water surface level, said generatorcomprising a spring having a tunable stiffness that produces electricalenergy using kinetic energy of the energy storage mass along the linearaxis.
 2. The marine device of claim 1 wherein the body is configuredsuch that the water surface level change causes movement of the bodyrelative to the water surface level.
 3. The marine device of claim 2wherein the moving portion is configured to linearly translate relativeto the portion of the body that rests above the surface level of water.4. The marine device of claim 1 wherein the mass is configured todisplace in a direction substantially opposite to a direction ofdisplacement for the body when the water surface level changes.
 5. Themarine device of claim 1 wherein the spring includes a stiffness thatprovides a resonant frequency for the mechanical energy transmissionsystem within about 0.2 hertz of a resonant frequency for the marinedevice.
 6. The marine device of claim 1 further comprising a secondenergy storage mass that is configured to move relative to the body inresponse to the water surface level change.
 7. The marine device ofclaim 6 further comprising a second generator configured to produceelectrical energy using kinetic energy of the second energy storagemass.
 8. The marine device of claim 1 wherein the mechanical energytransmission system is configured to rest above the surface level of thewater when the marine device floats in the water.
 9. The marine deviceof claim 1 wherein the device is a floating electrical energy generationdevice and includes a tether configured to transport electrical energyfrom the floating generation device.
 10. A marine device comprising; abody, wherein the marine device is configured such that a portion of thebody rests above a surface level of water when the marine device floats;a mechanical energy transmission system including a) a first energystorage mass that is configured to move relative to the body in responseto a water surface level change that causes tilting of the body relativeto the water surface level, wherein the first energy storage mass isconfigured to move at a first angle relative to a vertical center of thebody when the portion of the body rests above the water surface level,and b) a second energy storage mass that is configured to move relativeto the body in response to the water surface level change that causestilting of the body relative to the water surface level, wherein thesecond energy storage mass is configured to move at a second anglerelative to a vertical center of the body when the portion of the bodyrests above the water surface level; and at least one generatormechanically coupled to the first energy storage mass and to the secondenergy storage mass, said at least one generator comprising a springhaving a tunable stiffness that produces electrical energy using kineticenergy of the first energy storage mass and the second energy storagemass.
 11. The marine device of the claim 10 wherein the first energystorage mass is slideably coupled to a linear axis and the generator inconfigured to produce electrical energy using kinetic energy of thefirst energy storage mass along the linear axis.
 12. The marine deviceof claim 10 further comprising a spring mechanically coupled to thefirst energy storage mass and mechanically coupled to the body.